Smart interactive textile systems refer to an intelligent textile system that provides a smart environment for users by responding and reacting spontaneously to outside stimulus. In order to achieve smart interactive textile systems, there needs to be a textile infrastructure where sensors, actuators, power sources and data processing and communication devices are electrically interconnected. And further, these electrical devices should be applicable to textiles.
An electronic circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. The PCB, or Printed Circuit Board is at present a widely used electronic circuit, in which a conductive line or signal line is wet-etched on a dielectric substrate. PCB is sturdy, inexpensive and highly reliable, but it is rigid and heavy with space limitations. The FPCB or Flexible Printed Circuit Board improves these drawbacks by using copper-foiled polyimide films which bend flexibly. The FPCB, having advantages of being easy to form detailed patterns, flexible, light-weighted and of occupying less space, is widely applicable to display-related products such as LCD and PDP modules, etc. However, its complex manufacturing process leads to increased production cost and a harmful working environment. Moreover, its limited flexibility causes the copper foil to break after excessive deformation. Meanwhile, a project on stretchable electronics, or STELLA which is carried out by the EU for use in healthcare, wellness and functional clothes, has integrated electronics in stretchable parts and products. Stretchable electronics integrate electronic components, energy supply, sensors, actuators, or display and switches on a stretchable substrate such as silicon or polyurethane. However, the method does not involve textile processing and thus is not applicable in many applications of smart textiles.
U.S. Patent Publication No. 2006-0289469 discloses a flexible circuit that overcomes the shortcomings of the PCB or FPCB and works properly as part of wearable electronics. This prior art proposes materials embroidered with silver-coated nylon yarns and a flexible circuit made by etching silver-coated nylon fabrics in any desired shape. The circuit is flexible, light-weighted, and attachable to clothes. However, the silver-coated textiles have limitations in reducing the electrical resistance to a desired level. Therefore in order to reduce electrical resistance, a number of metal-coated fibers should be used or multiple layers of the fabric should be stitched. That is, the circuit consists inevitably of thick lines or thick patches, as the conductive yarn is too thin to provide desired conductivity. Consequently, when applied to clothes or other textiles, the circuit has poor washing and abrasion durability. And when the silver-coated yarns are coated with PVC for electric insulation, the circuit can not be directly used as an embroidery yarn but only used as an applique.
Thus a need exists for an electrically conductive embroidered circuit that has low electrical resistance with washing and abrasion durability, and adequate strength to maintain electric capability under external force.